For words that have only 3 letters, there's no 4th letter. As an example with the word “include”, there won't be any far more letters afterwards and thus need to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you would have employed “addi” for “addict”. https://madesocials.com/story4451547/the-invalid-bip39-phrase-diaries